This invention relates to apparatus for facilitating the machining or grinding of predetermined regions of workpieces.
In particular, the present invention is concerned with the grinding of the side faces of hard material tips mounted to the teeth of saw blades.
Machines are known for the grinding of the side faces of such tips whether on circular or linear i.e., band saws in which both side faces are ground in a single operation.
Generally, after the side faces of a tip have been ground the tooth tip is broadest at its leading i.e., cutting edge and diminishes in width from the leading edge to the rear face of the tip. In addition, the side face grinding is such that the tip tapers from the top face of the tip towards the bottom of the tip.
As is well known, the purpose of the side face grinding is to produce side faces which are mutually inclined at predetermined angles to the planes of the side faces of the blade body and teeth. In addition, generally speaking the grinding must be such that the side faces are symmetrically ground with respect to the blade body so that corresponding points on the both side faces of a tip are equidistant from the medial plane of the blade body, except where the grinding is intended to produce an asymmetrical arrangement. To achieve this it is important, during the grinding of the tips on the teeth on the blade, that the blade/tooth should not deflect from the required correct grinding position. Firmly clamping the blade against displacement with respect to the grinding wheels is necessary.
Following completion of the machining/grinding of each saw tip blade tooth, successively indexing the saw blade to bring the next tip to be machined to the location of the machine at which the side grinding wheels are able to grind the side faces is required. This position can be termed the grinding station. During this indexing operation the clamping of the blade has to be released so that the blade is free to be moved by an indexing finger or the like which is arranged to advance the next tooth whose tip is to be machined/ground to the grinding station. Indexing involves pushing against the tooth in question while at the same time guiding the blade through the blade clamping means. At the completion of the indexing operation the blade is reclamped to prevent movement of the blade.
In known machines the usual practice involves clamping the body blade well below the gullets of the teeth so that the clamping arrangements when released do not impede the indexing operation, and so that they do not impede operational movements of the grinding wheels themselves. This mode of clamping relies upon the strength of the blade body, assuming that grinding wheel pressures upon a tip will not distort the tooth with respect to the blade body. However, in practice distortion can occur, leading to an incorrectly machined tip.
A further difficulty arises in relation to the known clamping arrangements because with known machines it is necessary to remove the clamping arrangements from one side of the blade to enable a blade to be removed. In this connection it is convenient to bear in mind that some blades, especially band saw blades, can be twenty or more centimetres deep so that blade changing is a relatively complex and time consuming operation, particularly if it is not possible conveniently to remove the blade clamping arrangements.
As indicated above, an important requirement for the machining of saw blade tips is that their side faces should be machined or ground so that the resulting ground side faces are symmetrically positioned with respect to the medial plane of the saw blade body. In other words, it is usually required that each tip should project to the same extent to either side of this medial plane.
Hitherto it has been presumed that with the known machines and their associated blade clamping arrangements that this conditon of symmetry (when required) is always achieved even though before the grinding operation the tips may have projected unequally to opposite sides of a tooth tip. In other words, it has been assumed without respect to initial individual widths of the tips in relation to the saw blade body, after grinding the required dimensions and angles for the side faces had been achieved.
Industrial users of, for example, band saw blades, have been demanding thinner and thinner saw blades and associated tips so that the amounts of wood wasted during sawing operations such as reducing a tree trunk to planks is reduced. In addition, since one of the most effective materials for the production of saw blade tips, namely the material known under the trade name Stellite, is comparatively expensive, further consequence of thinner blades is that the tips will also be small/thinner in size, reducing the amount of Stellite required for each tip.
It has been found that the presently available clamping arrangements are not adequate for holding a saw blade during the side face grinding of tips on the teeth of saw blades which are thinner than those conventionally contemplated. Whenever a tip on such thin saw blades is not initially symmetrically positioned with respect to the medial plane of the blade body, the pressures exerted by the grinding wheels during grinding distorts the tooth with respect to the clamped blade body medial plane. Consequently where such distortion has occurred the tip remains effectively offset with respect to the medial plane of the blade body and the face angles may well be incorrectly formed since the grinding operation has not removed the excess thickness to one side of the blade. The use of such saw blades whose side faces are not ground to the correct angles and size are very inefficient in operation and become rapidly damaged.